The present invention relates to an exhaust gas recirculation (EGR) control device for an engine.
Conventionally, an EGR passage is formed to connect an exhaust passage with an intake passage of an engine, so as to recirculate a part of the exhaust gas of the engine from the exhaust passage to the intake passage. For example, JP2008-106658A discloses such an EGR passage. The EGR passage includes a high-pressure EGR passage and a low-pressure EGR passage. The high-pressure EGR passage connects an exhaust passage at a position upstream of a turbine of an exhaust turbocharger, with an intake passage at a position downstream of a compressor of the exhaust turbocharger. The low-pressure EGR passage connects the exhaust passage at a position downstream of the turbine of the exhaust turbocharger, with the intake passage at a position upstream of the compressor of the exhaust turbocharger. An idle operation continuation period of time of the engine is measured, and when the idle operation continuation time period is longer than a predetermined period of time, a low-pressure EGR amount which is a recirculation amount of exhaust gas through the low-pressure EGR passage is reduced and a high-pressure EGR amount which is a recirculation amount of exhaust gas through the high-pressure EGR passage is increased. Thus, a temperature decrease of a combustion chamber of the engine caused by a temperature decrease of low-pressure EGR gas which is recirculated by the low-pressure EGR passage is reduced.
Incidentally, in engines with small emission amounts, since heat generation is low, in a case where a configuration of supplying cooling water of the engine to a heater core of an air conditioner is adopted, it is difficult to supply a sufficient amount of heat to the heater core, causing a problem of degradation in heating performance, particularly during an idle operation of the engine.
Thus, an increase to the EGR amount, particularly the high-pressure EGR amount as JP2008-106658A, can be considered. However, if the EGR amount is increased with insufficient consideration, a problem arises that the emission performance degrades when accelerating the engine from the idle operation (particularly when accelerating the engine in the start of a vehicle on which the engine is mounted). Whereas if a fuel injection amount is reduced to avoid the degradation in the emission performance when accelerating the engine, the engine acceleration performance degrades.